1. The Field of the Invention
The present invention relates to a safety device used particularly in motor vehicles which, upon the onset of a collision, deploys an inflatable restraint cushion, known as an air bag cushion, to protect the occupants of the vehicle from the impact of the collision. More particularly, this invention relates to a positive lock assembly that is utilized in an air bag inflator assembly.
2. The Relevant Technology
An air bag system includes a gas generator commonly known as an inflator assembly. When a motor vehicle, usually an automobile, is involved in a collision, a crash signal actuates the air bag inflator assembly to cause an air bag cushion to deploy. Typically, the actuator triggers a chemical or pyrotechnic reaction in the inflator assembly. In a pyrotechnic-type inflator assembly, gas is produced by the burning of a gas-generating material. The reaction in the air bag inflator assembly produces an inert gas which is directed under pressure into the air bag cushion and forces the air bag cushion into the passenger compartment of the vehicle.
Initially, air bag inflator assemblies included a housing with three distinct chambers within the outside wall thereof. In general, there was an inner wall between the ignition system and the gas generating material and a second wall between the gas generating material and a filter. The gas produced in the inflator was required to flow through ports in both the inner wall and the second wall before exiting the housing through diffusion ports formed in the outside wall into an associated air bag cushion.
Air bag inflator assemblies were improved such that the housings now have an inner side wall and an outer side wall that are concentric. The housing also includes a pair of opposite end walls joined therewith to form a sealed enclosure for containing a solid gas generant material and an ignition system. The inner side wall forms a central ignition chamber that contains the ignition system. The inner side wall has a plurality of ignition ports that are in communication with a combination combustion and filter-containing chamber formed around the ignition chamber. A gas generant material and a filter are disposed in the combustion chamber. The outer side wall of the housing has a plurality of gas discharging, diffuser ports for gas generated in the inflator assembly to rapidly inflate an associated air bag.
Current designs of air bag inflator assemblies include an annular retainer disk that is positioned adjacent to the top wall of the inflator housing and covers the top of the inner side wall to prevent "blow by" of hot gases around the upper and lower end of the filter. In addition, the retainer disk holds the gas generate pellets in a relatively tight cohesive body so that vibrations do not harm the pellets over a long period of time of vehicle use before air bag deployment is required.
Current designs of the retainer disk and an inner side wall require the retainer disk to be to press or force fit over an end of the inner side wall. The inner side wall may comprise an ignition tube. The length of the igniter tube that can be utilized in the press fit assembly of the retainer disk and the igniter tube is limited by the requirement that the igniter tube has ignition apertures formed therethrough that are utilized when igniting the pellets contained in the inflator assembly. As a result, the length of the igniter tube which could be utilized in the press fit between the igniter tube and the retainer disk is small and does not have the strength to resist accidental bumps as well as vibrations. Consequently, with the current design of igniter tubes and retainer disks utilized in the inflator assembly, the connection between the igniter tube and the retainer disk is not particularly strong.
During the manufacturing and assembly process, the retainer disk has demonstrated a tendency to pop off the ignition tube prior to welding the inflator assembly. This is very disruptive to the assembly process, particularly if the gas generation material has been disposed in the inflator assembly. A spill of the gas generation material may even present a dangerous situation. In addition, accidental separation of the ignition tube and the retainer disk during the life of the air bag impedes the effectiveness of the inflator assembly.
Attempts have been made to resolve the current problems resulting from the accidental separation of the igniter disk and the ignition tube. One proposed solution to the problem was to crimp the retainer disk around the ignition tube. Crimping, however, requires exerting a non-vertical force, using such equipment as a non-vertical press head, to apply radial force to the retainer disk to obtain a positive or mechanical lock between the igniter tube and the retainer disk. The application of radial force requires expensive tooling and the addition of unconventional assembly procedures to the assembly process.